In recent years, semiconductor solid-state lighting has become the fourth-generation light source due to its advantages of high luminous efficiency, long shelf-life, non-pollution and good shock-resistance. Currently, white light-emitting diode (LED) is mainly achieved in two main approaches: in the first approach, a white light-emitting diode (LED) is prepared by packaging red LED, green LED and blue LED in one light source, namely a multi-chip white LED; in the second approach, a white light-emitting diode (LED) is prepared by using a single LED chip in combination with the use of phosphor to achieve white light, namely phosphor converted LED. Due to such defects as color drift, complexity in control circuit and high production cost etc. of the first approach, the second approach is usually adopted in the field of lighting. Currently, phosphor for white LED is mainly present in the form of three systems: 1) aluminate; 2) silicate; 3) nitride (oxide).
Silicate system is one important class of luminescent material, which not only has a high luminous efficiency under UV, near UV and blue light excitation, but also has a high chemical stability. In addition, the luminous range of the silicate system may cover from green light zone to orange-red light zone, so as to compensate for the deficiency of YAG:Ce3+ powder in the red light zone, and therefore the colour rendering index of LED can be effectively improved.
Silicate phosphors Sr2SiO4:Eu2+ and Sr3SiO5:Eu2+ were reported by G. Blasse (see Philips Res. Rep., vol. 23, pages 189-200) in 1968, and luminance thereof was also researched. The excitation spectra of both Sr2SiO4:Eu2+ and Sr3SiO5:Eu2+ range from 250 to 550 nm, with emission peaks of around 560 nm and 580 nm, respectively. Thereby, Sr2SiO4:Eu2+ and Sr3SiO5:Eu2+ can be used in combination with UV LED, near-UV LED and blue LED for the preparation of a light source. However, both Sr2SiO4:Eu2+ and Sr3SiO5:Eu2+ phosphors have poorer thermostability, and quenching temperature thereof is found at around 390K and 460K, respectively. When silicate phosphors Sr2SiO4:Eu2+ and Sr3SiO5:Eu2+ are packaged into an LED light source for operation, part of electric energy is converted into light energy, while the other part is converted into heat energy, thereby rendering a temperature rise in a pn junction, which causes luminance attenuation of the phosphor packaged in the pn junction. Therefore, luminous flux of the LED light source reduces, and in turn luminous efficiency of the same decreases. Accordingly, improvement in the thermostability of such silicate is particularly important to their application.